1. Field of the Invention
The present invention relates to a pixel structure of a thin film transistor liquid crystal display and a fabricating method thereof. More particularly, the present invention relates to a pixel structure of a thin film transistor liquid crystal display fabricated in four mask processes.
2. Description of the Related Art
A thin film transistor liquid crystal display mainly comprises a thin film transistor array substrate, a color filter array substrate and a liquid crystal layer sandwiched between the two substrates. The thin film transistor array substrate has a plurality of pixel structures, and each pixel structure comprises a thin film transistor and a pixel electrode.
The pixel structure of most of the thin film transistor liquid crystal display is fabricated in five mask processes. The first mask process is used to pattern a first metallic layer so as to form a scanning line and a gate electrode of the thin film transistor. The second mask process is used to define a channel layer and an ohmic contact layer of the thin film transistor. The third mask process is used to pattern a second metallic layer to form a data line and a pair of source/drain electrodes of the thin film transistor. The fourth mask process is used to pattern a passivation layer and the fifth mask process is used to pattern a transparent conductive layer to form a pixel electrode.
However, as the size of thin film transistor liquid crystal display panel continues to increase, several problems such as a drop in the yield and throughput have to be overcome. Therefore, if the number of mask processes for forming the thin film transistor is reduced, that means the number of exposure process in fabricating the thin film transistor is reduced, the manufacturing time and cost can be reduced.
At present, methods of fabricating thin film transistor liquid crystal display using four mask processes have been developed. However, these methods often utilize a halftone pattern design on a photo-mask to achieve the reduction of one mask process. However, using the halftone pattern on a photo-mask to form the display also exists some problems. For example, it is more difficult to design the pattern layout on the photo-mask and the photoresist selectivity should be considered seriously. Furthermore, using the photo-mask having a halftone pattern thereon to perform an exposure process usually causes the patterned photoresist to have non-uniform patterns.